Apparently the Canada Industrial Relations Board found this strike illegal because 72 hours strike notice wasn't given. However that seems strange because it's not a new strike, it's the previous strike resuming after a potential agreement was voted down. Regardless, don't expect this to be the end of things.
I don't expect ANY union to call off a strike in the future unless and until any new offer is ratified. No 'good faith' get-back-to-work action ever again.